8000 Fix crash when a star expression is used in isinstance by onlined · Pull Request #6659 · python/mypy · GitHub
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Fix crash when a star expression is used in isinstance #6659

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Merged
merged 6 commits into from
Apr 12, 2019
Merged

Fix crash when a star expression is used in isinstance #6659

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19572a7
Fix
onlined Apr 11, 2019
704cf27
Add tests
onlined Apr 11, 2019
8d20e81
Remove empty lines
onlined Apr 11, 2019
42e0929
Remove accidentally added file
onlined Apr 11, 2019
80d7811
Improve tests
onlined Apr 12, 2019
4d0126c
Remove extra blank lines
ilevkivskyi Apr 12, 2019
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2 changes: 2 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3949,6 +3949,8 @@ def flatten(t: Expression) -> List[Expression]:
"""Flatten a nested sequence of tuples/lists into one list of nodes."""
if isinstance(t, TupleExpr) or isinstance(t, ListExpr):
return [b for a in t.items for b in flatten(a)]
elif isinstance(t, StarExpr):
return flatten(t.expr)
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Technically this adds some non-trivial functionality. Could you please add tests that check the behavior (i.e. whether types are narrowed or nor) for situations like:

isinstance(x, *(str, int))  # This should fail IIUC
isinstance(x, (int, *(str, list)))  # This should behave the same as (int, str, list)

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@onlined onlined Apr 11, 2019 •
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I did not understand the difference between the second one and my proposed test.

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Basically your test only tests that mypy doesn't crash, while I want:

  • check that type narrowing happens when it should, and doesn't happen when it shouldn't
  • check both situations where tuple appears in place and where it is referenced by a variable

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I got it, thanks.

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Done.

else:
return [t]

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26 changes: 26 additions & 0 deletions test-data/unit/check-isinstance.test
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Expand Up @@ -2207,3 +2207,29 @@ def bar(x: Union[List[str], List[int], None]) -> None:
assert isinstance(x, list)
reveal_type(x) # E: Revealed type is 'Union[builtins.list[builtins.str], builtins.list[builtins.int]]'
[builtins fixtures/isinstancelist.pyi]

[case testIsInstanceWithStarExpression]
from typing import Union, List, Tuple

def f(var: Union[List[str], Tuple[str, str], str]) -> None:
reveal_type(var) # E: Revealed type is 'Union[builtins.list[builtins.str], Tuple[builtins.str, builtins.str], builtins.str]'
if isinstance(var, (list, *(str, int))):
reveal_type(var) # E: Revealed type is 'Union[builtins.list[builtins.str], builtins.str]'
[builtins fixtures/isinstancelist.pyi]

[case testIsInstanceWithStarExpressionAndVariable]
from typing import Union

def f(var: Union[int, str]) -> None:
reveal_type(var) # E: Revealed type is 'Union[builtins.int, builtins.str]'
some_types = (str, tuple)
another_type = list
if isinstance(var, (*some_types, another_type)):
reveal_type(var) # E: Revealed type is 'builtins.str'
[builtins fixtures/isinstancelist.pyi]

[case testIsInstanceWithWrongStarExpression]
var = 'some string'
if isinstance(var, *(str, int)): # E: Too many arguments for "isinstance"
pass
[builtins fixtures/isinstancelist.pyi]
0